A common or electrical bus is used in a variety of applications including work machines, vehicles and computers. Electrical buses may also be used in high voltage applications to deliver power from a power source to the electrical devices. An electrical bus is essentially a parallel circuit that is used to connect a plurality of electrical devices together with a power source including generators, solar cells, batteries, or the like. Moreover, electrical buses may be used in direct current (DC) applications and have a positive line and a negative line, or ground line, over which a potential voltage difference may be provided.
As the electrical devices and subcomponents of an electric drive machine rely on the common bus for power, it is essential to regulate or maintain the bus voltage throughout operation of the machine for proper functionality. It is well known that a generator, such as a switched reluctance (SR) generator driven at relatively low engine idle speeds, may be used to regulate the common bus voltage during normal operations of the associated machine. However, it is also well known that such a generator cannot be used to regulate the voltage across a common bus without first priming the common bus or providing a startup voltage thereto. For instance, if the bus voltage has been substantially discharged and/or is less than the minimum startup voltage required for priming the generator, the generator may be unable to turn and begin regulating the bus voltage upon the next startup without additional help.
Accordingly, typical high voltage electric drive machines are provided with an auxiliary voltage source, such as an accessory power converter, configured to prime the common bus and the generator during startup. For example, once the engine of the machine is started by an operator, the accessory power converter is also started to charge the common bus and generator to the minimal startup voltage required. Once the engine idle speed settles to a relatively low idle speed and stabilizes, a request may be submitted to the generator to begin regulating the common bus to an optimum bus voltage. As the common bus and generator have already been primed or charged by the accessory power converter, the generator may begin regulating the bus voltage as soon as the request is received. Once the common bus voltage has been regulated, the operator may be enabled to change the throttle position, engage the engine into a relatively high idle speed and commence normal operations of the machine.
Although such priming strategies may be adequate for most purposes, a significant problem may arise if the accessory power converter, or auxiliary voltage source, malfunctions. For instance, if the auxiliary voltage source fails to prime the common bus or generator during startup of a high voltage electric drive machine, the common bus may not have the minimum charge that is required to start the associated SR generator. Moreover, without a properly primed common bus, the SR generator may be unable to regulate the common bus to the appropriate bus voltage and/or distribute the proper DC voltage to the electrical devices of the machine that are connected to the common bus.
The disclosed system and method is directed at overcoming one or more of the problems set forth above.